Loss of CoREST (RCOR1) induces HSPC expansion. (A) Schematic representation of the experimental strategy to knockout RCOR1. (B) RCOR1 protein levels in UCB CD34⁺ cells edited with nontargeting (Nt) control or RCOR1 guides (day 10). (C) FACS plots showing the frequency of CD34⁺ and EPCR⁺ populations in Nt control and RCOR1-knockout UCB HSPCs (day 10). The relative number of CD34⁺ cells (D) and CD34⁺EPCR⁺ cells (E) in RCOR1-knockout HSPCs compared with the Nt control–treated cells over time. Total cell numbers for each condition and time point were calculated and normalized to the mean of the control Nt sgRNA. Data from 3 replicates from 1 of 2 independent experiments with similar results. (F) Relative change in frequency of GFP⁺ cells over time in Nt control and RCOR1-edited samples compared with day 4 (D4) in DMSO- or UM171-treated cultures. Values are normalized to the NT DMSO control (n = 3). *P ≤ .05, ****P ≤ .0001.